a principal line or route of a railroad, as contrasted with a branch or secondary one.
a principal highway.
Slang.
a prominent and readily accessible vein of the body that may be used for a narcotic's injection.
the act of mainlining.
a fashionable residential district west of Philadelphia.
any fashionable district where socially prominent people live.
railways
the trunk route between two points, usually fed by branch lines
( as modifier )
a main-line station
a main road
First recorded in 1835–45
Examples are provided to illustrate real-world usage of words in context. Any opinions expressed do not reflect the views of Dictionary.com.
It has only once been shut for longer since it opened in 1886 - that was when electric wires were installed 10 years ago as part of the £2.8bn south Wales main line electrification project.
From BBC ● May 22, 2026
The depletion of mangrove forests along the shoreline - the coast’s main line of defence against erosion - is to blame.
From BBC ● Aug. 13, 2024
The extensive corroborating evidence is just one way the prosecution is cutting off the defense’s main line of attack.
From Los Angeles Times ● May 2, 2024
The service was established by Congress as the main line of defense for children who are exploited online.
From Seattle Times ● Apr. 22, 2024
Off to their left, Frank could see the main line of the Fifth Cohort advancing in turtle formation, shields forming a shell over their heads and sides.
From "The Son of Neptune" by Rick Riordan
In suburbs including Philadelphia’s Main Line, moms and dads are pleading with districts to rein in tech: “These electronics have ruined parenting.”
From The Wall Street Journal ● Jun. 22, 2026
Under current plans, HS2 trains will travel from Birmingham to Manchester, but at reduced speed on the existing West Coast Main Line.
From BBC ● Mar. 23, 2026
Cardinale grew up in Villanova, Penn., an affluent suburb on Philadelphia’s Main Line, and attended The Haverford School, an all-boys prep school.
From The Wall Street Journal ● Jan. 16, 2026
The operator said services along the Highland Main Line, between Inverness and Perth, was running.
From BBC ● Jan. 5, 2026
It’s on the prestigious Main Line, just twenty-five minutes outside Philadelphia, on a rolling campus surrounded by overgrown foliage.
From "The Other Wes Moore: One Name, Two Fates" by Wes Moore
Definitions and idiom definitions from Dictionary.com Unabridged, based on the Random House Unabridged Dictionary, © Random House, Inc. 2023
Idioms from The American Heritage® Idioms Dictionary copyright © 2002, 2001, 1995 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company.
